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I recently had my oil changed on my 2004 Buick Century. Does overfilling the oil level harm the engine?

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In most engines the surface of the oil in the oil pan is close to the crankshaft. If the oil is overfilled to the point that the crankshaft hits the oil, it can cause the oil to form foam. This will in turn decrease the efficiency of the oil pump, which will be pumping a mixture of air and oil. This means that parts that depend on the oil pump for lubrication won't be getting as much oil as they're designed to work with, which will cause premature wear.

Edit: I'm not sure why the downvote, as this is a perfectly valid and accurate description of what happens when the crankshaft hits the surface of the oil and agitates it. For references: this article describes oil-lubricated machines in general; this is from Car Talk; and this is a Google books excerpt describing how the crankshaft can agitate the oil thus causing foaming. It is the paragraph under Oxidation Inhibitors and describes how foaming can cause tar formation, which I omitted from my original post.

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  • I apologize very much. I was using my phone app and literally hit the downvote button without realizing it. I changed it and up-voted you! This is definitely a valid answer, and I apologize once again! >_<!!
    – cloudnyn3
    Feb 9, 2016 at 17:33
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You can run into a few problems with over-filling your engine oil. It depends on how much you overfilled your oil pan. A half a quart over is ok. If you put an entire quart or more over, this could be a real problem.

When you over-fill to that extent it can cause issues with gaskets being subjected to pressures they were not designed to be subjected to. There could also be various bearings and moving components such as your connecting rods and rod bearings that don't necessarily need to be soaked in oil to function. Over-filling could actually hinder their function.

Over-filling can also hinder the function of hydraulic components like VTEC on many Hondas. You can also Over-Fill the pan until the point of touching the bottom of your pistons. They will burn oil if filled too much. You could end up with sediment and by-product in the cylinders do to this. This is just a few examples of what can happen if you over-fill your oil pan. There are many more negative things that could result from this. I hope this helps you!

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